Video footage of the crash site broadcast on state television showed a huge crevice created by the plane, a Russian-built TU-154 that appeared to have splintered on impact.

"Evidence shows that the plane has broken into pieces and all the passengers on board are feared dead," Gen. Massoud Jafari-Nasab told the official Islamic Republic News Agency.

The flight crashed 16 minutes after departure, Jafari-Nasab told the semi-official Fars news agency. Reza Jafarzadeh, spokesman for the state aviation company, told Iranian television that 153 passengers and 15 crew members were aboard.

Witnesses told the Iranian news agency the plane was on fire as it hit the ground.

"Its wheels were out and there was fire coming from the lower parts," Abul-Fazel Idaji told Fars. "Moments later the plane hit the ground and broke into pieces."

Among those presumed dead were 10 members of the Iranian national youth judo squad traveling to Yerevan for a summer training camp.

"We need to investigate all the factors contributing to the incident before giving further details on how the incident took place and making an expert comment," Jafarzadeh said.

Iran's Armenian ethnic minority has strengthened its ties to neighboring Armenia in recent years. Tehran and Yerevan have strong commercial and political ties.

Armenian President Serzh Sargsyan cut short a trip to the provinces and returned to the capital as the crash was announced on public television. Yerevan's civil aviation department set up a headquarters to begin a probe of the crash, the organization's leader, Nelly Cherchinyan, told the Mediamax news agency.

In Yerevan, the deputy head of the Armenian civil aviation organization told reporters the pilot attempted an emergency landing after an engine caught fire.

But an unnamed airline representatives told Armenian television that officials were still trying to assess the cause of the crash and sort out the names and nationalities of the passengers.

"The information regarding citizenship is being clarified with the help of border guards in Tehran," the representative said. "There is nothing [to report] on the reasons [for the crash], nothing; no theories, no statements."

Caspian, a 16-year-old commercial airline, operates within Iran and to Syria, Turkey, Ukraine, the United Arab Emirates and Armenia, using Russian-made Tupolev jets that many Iranians fear are prone to malfunction.

Experts described the TU-154 plane as the Russian equivalent of the Boeing 727. The U.S. has long maintained sanctions on the sale of commercial aircraft and plane parts to Iran, a posture that many Iranians say puts the lives of ordinary travelers at risk.